Remove outdated languages from Ubuntu’s Firefox

Always on the bleeding edge I like to use beta versions of upcoming Ubuntu releases. This sometimes poses a little problem: More often than not, there come outdated language definitions with Firefox, causing some minor annoyances.
The biggest annoyance of which is that you just can’t seem to delete those offending addons:

firefox-undeleteable-addons

The solution, albeit simple, is harder to find:

{openx:6}

Just open a terminal window and switch to superuser mode using

sudo -i

, then start Firefox from the command line using

firefox

. One Firefox is running, just open the Addon window, et voila:

firefox-removable-addon

Now you can remove any addon you like, even those that were locked before.